Passwords can be written as plain text in SQL statements such as CREATE USER, GRANT, SET PASSWORD, and statements that invoke the PASSWORD() function. If such statements are logged by the MySQL server as written, passwords in them become visible to anyone with access to the logs.

Statement logging avoids writing passwords as cleartext for the following statements:

CREATE USER ... IDENTIFIED BY ...
GRANT ... IDENTIFIED BY ...
SET PASSWORD ...
SLAVE START ... PASSWORD = ...
CREATE SERVER ... OPTIONS(... PASSWORD ...)
ALTER SERVER ... OPTIONS(... PASSWORD ...)

Passwords in those statements are rewritten to not appear literally in statement text written to the general query log, slow query log, and binary log. Rewriting does not apply to other statements. In particular, INSERT or UPDATE statements for the mysql.user system table that refer to literal passwords are logged as is, so you should avoid such statements. (Direct modification of grant tables is discouraged, anyway.)

For the general query log, password rewriting can be suppressed by starting the server with the --log-raw option. For security reasons, this option is not recommended for production use. For diagnostic purposes, it may be useful to see the exact text of statements as received by the server.

Contents of the audit log file produced by the audit log plugin are not encrypted. For security reasons, this file should be written to a directory accessible only to the MySQL server and users with a legitimate reason to view the log. See Section 6.4.4.2, “MySQL Enterprise Audit Security Considerations”.

To guard log files against unwarranted exposure, locate them in a directory that restricts access to the server and the database administrator. If the server logs to tables in the mysql database, grant access to those tables only to the database administrator.

Replicas store the password for the replication source in the source info repository, which can be either a file or a table (see Section 17.2.2, “Relay Log and Replication Metadata Repositories”). Ensure that the repository can be accessed only by the database administrator. An alternative to storing the password in a file is to use the START SLAVE statement to specify credentials for connecting to the source.

Use a restricted access mode to protect database backups that include log tables or log files containing passwords.